1. Field of the Invention
This invention relates to a method for removing boron from polyalkyl hydroxyaromatic compounds. More particularly, this invention relates to removing boron from boron trifluoride-catalyzed polyalkyl hydroxyaromatic reaction products to levels below about 10 parts per million (ppm) by filtering the polyalkyl hydroxyaromatic reaction product with a solid filtering agent having an active surface.
2. Description of the Related Art
Boron trifluoride is used as a catalyst in relatively low concentrations for synthesis of liquid hydrocarbons from various olefins. Example applications are alkylation of hydroxyaromatic compounds with various olefins, oligomerization of alpha olefins, and polymerization of low molecular weight olefins. Many of these products find application in lubricating oil additives and gasoline or diesel fuel additives. The boron trifluoride may be introduced into the reaction as a gas or as a complex (for example, boron trifluoride-etherate, boron trifluoride-phenol, and many others). Depending on the particular process, the boron trifluoride is present in the reaction mixture as dissolved gas, or a coordination compound or a mixture of the two forms.
A common feature of all of these processes is that the boron trifluoride must be removed after the reaction, either in a form that can be recycled or in a form that requires disposal. Depending upon the molecular weight and the viscosity of the product, further processing such as distillation can be limited by the presence of boron trifluoride in the product because it will cause depolymerization and cracking of olefin polymers at elevated temperatures. There have been three general techniques used that may or may not involve chemical reaction of the boron trifluoride; adsorption on a particulate solid and separation from the reaction product, extraction using various aqueous solutions and phase separation from the reaction product, and removal by distillation or stripping. Combination of these processes can also be used.
U.S. Pat. No. 4,045,507 describes a process in which 1-decene is oligomerized to a product containing primarily trimer and tetramer in a reactor pressurized with boron trifluoride and containing a coordination compound formed by complexing boron trifluoride with a suitable polar compound such as n-butanol. The resulting oligomer product solution contains boron trifluoride that must be separated from the product. U.S. Pat. No. 4,433,197 discusses a method of selective removal of the boron trifluoride from oligomer product leaving behind the polar compound (n-butanol) used to form the coordination compound. The boron concentration was reduced to a concentration of 13-32 ppm from an initial concentration of 0.5% using silica as a solid absorbent. Recovery of the boron trifluoride was then accomplished by extraction from the silica using n-butanol. A bed of granular polyvinyl alcohol was shown in U.S. Pat. No. 4,384,162 to be another effective adsorbent for nondestructive removal and recycle of boron trifluoride.
U.S. Pat. No. 3,917,733 gives a process scheme for removing boron oxide hydrate from a liquid aromatic hydrocarbon stream and the boron trifluoride off-gas from the alkylation zone using a moving bed of particulate alumina. No mention is made of recovering the boron trifluoride.
Solid reactants that neutralize and extract the boron trifluoride from reaction product have also been widely illustrated in the patent literature. In a 1-olefin oligomerization process, U.S. Pat. No. 4,981,578 discloses that potassium fluoride (KF) in either particulate solid or aqueous solution form can be reacted with the boron trifluoride (BF.sub.3) in the oligomer product solution. This reaction yields a solid precipitate of potassium fluoborate (KBF.sub.4) that can then be filtered from the oligomer product. The aqueous solution approach reduced the boron from an initial level of 820 ppm in the oligomer product to 63 ppm after treatment. Similarly, a bed of KF reduced the boron concentration from 820 ppm before treatment to 6 ppm after treatment. This patent teaches that sodium fluoride (NaF) or ammonium fluoride (NH.sub.4 F) may also be used instead of KF.
In a cracked-petroleum-fraction olefin polymerization process, U.S. Pat. No. 3,371,075 illustrates the use of particulate hydrated lime and fuller's earth (more than 90% natural attapulgite and montmorillonite) for neutralization and removal of boron trifluoride catalyst as well as decolorization of the product. The crude product containing the boron trifluoride is mixed with the hydrated lime and fuller's earth and then filtered. Boron was reduced from an initial concentration of approximately 540 ppm to about 4 ppm in the finished product.
In another 1-olefin oligomerization process using boron trifluoride, U.S. Pat. No. 4,956,513 discloses a simple water extraction method for directly removing boron trifluoride. In this method the crude product is washed with water and the phases separated. This is done twice and the aqueous phase washings are combined, then distilled to concentrate the BF.sub.3 --H.sub.2 O complex and recover water and n-butanol overhead. BF.sub.3 can then be recovered by mixing concentrated oleum or sulfur trioxide with the distillation bottoms.
Examples of water extraction applied to boron trifluoride removal from crude polyisobutylphenol, made from alkylation of phenol with polybutene, can be found in U.S. Pat. Nos. 5,300,701, 5,876,468, and British Patent GB 1,159,368. In the examples in these patents, the crude product is mixed with aqueous ammonia to neutralize the BF.sub.3 and then the product is extracted several times with water. The British Patent GB 1,159,368 further teaches that the BF.sub.3 can be neutralized with ammonia gas and then the BF.sub.3 --NH.sub.3 salt filtered from the crude polyisobutyl phenol.
Distillation techniques have also been used for boron trifluoride recovery of the 1-olefin oligomerization reaction mixture. In U.S. Pat. No. 4,263,467, the crude oligomer mixture exits the reaction zone and is then fed downward through a column packed with Berl saddles, a trickle-bed column, while maintaining a pressure of 203 mm of mercury on the column at 23.degree. C. The boron trifluoride is recovered overhead as a gas. The concentration of BF.sub.3 in the product is reduced from an initial level of 2.77% to a concentration after stripping of 680 ppm.
Another distillation approach to recover BF.sub.3 catalyst is disclosed in U.S. Pat. No. 3,000,964 for a phenol alkylation process. In this method, an entrainer constituent such as heptane is refluxed in the crude alkyphenol distillation column. The entrainer distills overhead and carries the BF.sub.3 overhead with it. The entrainer is returned to the column while the BF.sub.3 is absorbed into liquid phenol that is used to transport the BF.sub.3 back to the alkylation reactor. The alkylphenol is the distillation column bottoms product. There is no mention in this patent of residual boron concentration in the product or subsequent treating to remove trace contaminants.
The removal of alkaline catalysts from various polyether polyols is also known in the art. For example, U.S. Pat. No. 4,528,364 to Prier discloses a method of removing alkaline catalysts from polyether polyols and polyalkylene carbonate polyols which comprises dissolving the polyol in an aprotic solvent and then contacting the polyol solution with a sufficient amount of an adsorbent to adsorb the alkaline catalysts, followed by physically separating the adsorbent from the polyol solution. This patent teaches that the process described therein is advantageous as there is no water present to hydrolyze either the polyether polyol or the polyalkylene carbonate polyol. This patent further teaches that preferred adsorbents are aluminum and alkaline earth metal silicates, with magnesium silicate being most preferred. Suitable catalysts taught by this patent include alkali metal borates, alkaline earth metal borates and ammonium borates.
U.S. Pat. No. 4,507,475 to Straehle et al. discloses a process for purifying crude polyether polyols prepared by anionic polymerization of alkylene oxides in the presence of basic catalysts, wherein the polyols are mixed with water and ortho-phosphoric acid in certain quantity ratios, an adsorption agent is incorporated in the reaction mixture, the mixture is filtered and the water is removed from the polyol by distillation. This patent teaches that the polyol is mixed with 0.2 to 1.5 parts by weight of water per 100 parts of polyol and that the water content is of decisive important for the quantity of the purification. This patent further teaches that commonly used catalysts are alkali alkoxides and alkali hydroxides, preferably potassium hydroxide. Preferred adsorption agents taught by this patent are natural and synthetic silicas of earth alkali metals or aluminum, preferably synthetic magnesium silicate. This patent also teaches that it is advantageous to use filtration aids such as perlite, kieselguhr and diatomaceous earths, in addition to the adsorption agents.
U.S. Pat. Nos. 5,003,111 and 5,055,496, both to Harper, disclose a process for preparing polyether polyols by polymerizing isobutylene oxide with other alkylene oxides in the presence of an alkali metal catalyst and a crown ether cocatalyst to afford polyols containing low levels of unsaturation. These patents teach that the alkali metal may be derived from any suitable source, including alkali metal hydroxides, alkoxides and phenoxides, and that the alkali metal is preferably potassium or sodium. These patents further teach that the crude polyether polyol is treated to separate the alkali metal and crown ether from the product and that contacting the crude polyol with an adsorption agent, such as magnesium silicate, effectively reduces the alkali metal and crown ether content to acceptable levels. In the examples, these patents teach that the crude polyol was treated with 4% magnesium silicate, 0.5% water and 1% diatomaceous earth for four hours at 110.degree. C. to remove potassium hydroxide and crown ether. The polyol was then filtered through diatomaceous earth, diluted with toluene, water washed and vacuum stripped to provide the final polyol.
Japanese Kokai (laid-open) Patent Application No. HEI 3-195728 (1991) discloses a process for the purification of polyoxyalkylene polyol which has been synthsized in the presence of alkaline catalyst, which involves neutralizing the crude polyol with mineral acid to a pH of 4.5 to 7.5, followed by adsorption with a synthetic magnesium silicate containing less than 0.5 weight percent sodium, wherein the amount of synthetic magnesium silicate used as adsorbent is 0.05 to 5 weight percent of the polyol. The catalysts used in the polyol synthesis are described as potassium hydroxide, sodium hydroxide, potassium alcoholate, sodium alcoholate, potassium carbonate, sodium carbonate, metallic potassium and metallic sodium.
Japanese Kokai (laid-open) Patent Application No. HEI 4-197407 (1992) discloses a process for the purification of polyethers, in which catalyst is removed from crude polyethers having a high viscosity, which involves an adsorption treatment performed by the addition of a magnesium silicate adsorbent having an average particle diameter of above 100 micrometers to the crude polyether product, followed by filtration through a filter precoated with a filter aid consisting of diatomaceous earth having an average particle diameter of more than 100 micometers. Catalysts disclosed for use in the synthesis of the crude polyethers include alkaline catalysts, such as potassium hydroxide and sodium hydroxide, and complex metal cyano compounds, such as zinc hexacyano cobaltate complex and zinc hexacyano iron complex. The complex metal cyano compounds are preferred for making polyether polyols of 8,000 to 50,000 molecular weight.
Japanese Kokai (laid-open) Patent Application No. HEI 9-176073 (1997) discloses a process for manufacturing a propenyl ether compound in which an allyl ether compound is subjected to a rearrangement reaction with the use of an alkali metal hydroxide and/or alkaline earth metal hydroxide as a catalyst, wherein a silicate type adsorbent is used for catalyst removal and purification. This publication teaches that the adsorbent may be selected from acid clay, zeolite, synthetic magnesium silicate, synthetic aluminosilicate, and synthetic magnesium aluminosilicate. This publication further teaches that improved efficiency of catalyst removal can be obtained by the addition of water during the catalyst removal and purification period, wherein the weight ratio of water to silicate adsorbent is from 20:100 to 500:100.
It is known in the art that trace concentrations of contaminants remaining in an intermediate after synthesis can have a very detrimental effect on downstream processing. A good example of this problem is illustrated in U.S. Pat. No. 4,587,307. It is well known that polyisobutene is an intermediate in the manufacture of additives for lubricating oil and fuel applications. In one such use, polyisobutene can be combined with maleic anhydride to give a long-chain succinic anhydride. This can then be further derivatized with amines or polyamines to give the corresponding amides or imides. However, polyisobutenes obtained, for example, by the process described in U.S. Pat. No. 4,152,499 contain small quantities of substances not known in detail. These substances are present in the polyisobutene after the removal of the BF.sub.3 catalyst and readily volatile constituents. When the polyisobutene is used in a reaction with maleic anhydride, these unknown substances also react with the maleic anhydride forming deposits on the walls and internal parts of the reaction vessels. This results in reduced product quality and problems in maintaining the operability of the equipment. U.S. Pat. No. 4,587,307 addresses this problem by utilizing a method for treating the polyisobutene over a bed of solid adsorbent at 50-280.degree. C. The adsorbents include aluminum oxide, partially or fully hydrated aluminum oxide, boron oxide, partially or fully hydrated boron oxide, titanium oxide, partially or fully hydrated titanium oxide, or any combination of this group. Completely or partially hydrated silicon dioxide may be used at 20-280.degree. C.
An example in U.S. Pat. No. 4,587,307 describes a polyisobutene of number average molecular weight 1000 that was prepared by polymerization of isobutene at 20.degree. C. using 0.2 mole % BF.sub.3 as a catalyst. The polymer was freed from the catalyst in what is described as a "conventional manner" but no details were given in the patent example. However, the background section of this patent defines "conventional manner" as encompassing termination of the polymerization by adding water or an alcohol; filtering off solid residues or adsorbing them onto an adsorbent such as aluminum oxide; or, as an alternative, extracting catalysts with water, a base or methanol. In the patent example, low molecular weight constituents were removed by distillation at 200.degree. C. and subatmospheric pressure. The polyisobutene was then passed through a bed of acidic Al.sub.2 O.sub.3 having a mean particle size of 0.15 mm. The mean contact time was 20 minutes. No deposits were formed on the reaction vessel walls when a sample of this polyisobutene was reacted with maleic anhydride at 225.degree. C. in a stainless steel autoclave for 4 hours. By comparison, in a controlled experiment, polyisobutene that had not been treated with the acidic Al.sub.2 O.sub.3 led to the formation of deposits in the reaction with maleic anhydride.